This invention relates to a method of treating an instrument having an electrode and particularly to an instrument where the electrode is of the wire type operating in a gaseous atmosphere.
The method is particularly, although not exclusively applicable to instruments of the kind used to operate as counters for scattered or direct radiation from x-ray or other radiation sources where the instrument is basically used as a counter for the rays received.
One particular type of application of such instrument is an x-ray instrument of the type which is employed in coal preparation plants to determine quickly and efficiently the ash content of coal being processed by the plants.
The instrument is used in conjunction with an x-ray source which beams x-rays at a sample of the coal passing through the plant and the backscatter from the surface of the coal is collected in the instrument and a pulsed output is produced which can be analysed to give an exact determination of the percentage of ash and other material in the coal.
This type of instrument is also used to determine the quantity of iron or sulphur in coal depending on the setting of the instrument.
The active element in one common form of instrument comprises tungsten anodes sealed in an aluminum housing having a window which is transparent to x-rays. The housing is filled with an atmosphere of an inert gas such as argon which may also include a small amount of quenching gas such as methane. High tension connectors are connected to these anodes and lead from the housing to a suitable analysing device.
The anodes detect particularly when there is an iron fluorescence peak of x-rays and the sharper that this peak is the more effective the counter. The peak is a result of the anodes reacting to the x-rays generating their own current.
It has been found that after a period of time the peak begins to diminish and the instrument therefore becomes less effective and accurate. Furthermore, the response not only over the energy range of the iron peak but over the whole of the range of the instrument falls off and this may be due to the element becoming sullied. It is then necessary for the active element of the counter to be replaced and this can be an expensive operation.